<!DOCTYPE html>
<html lang="zh-CN">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>画板</title>
    <link rel="stylesheet" href="style.css">
</head>

<body>
    <canvas id="canvas" width="100" height="100"></canvas>
    <script>
        let canvas = document.getElementById("canvas");
        canvas.width = document.documentElement.clientWidth
        canvas.height = document.documentElement.clientHeight
        let ctx = canvas.getContext("2d");
        ctx.fillStyle = "black";
        ctx.strokeStyle = 'black'
        ctx.lineWidth = 8;
        ctx.lineCap = "round";

        let painting = false
        let last

        var isTouchDevice ='ontouchstart' in document.documentElement;
        if(isTouchDevice){
            canvas.ontouchstart = (e) => {
                let x = e.touches[0].clientX
                let y = e.touches[0].clientY
                last = [x , y]
            }
            canvas.ontouchmove = (e) => {
                let x = e.touches[0].clientX
                let y = e.touches[0].clientY
                drawLine(last[0] , last[1] , x , y)
                last = [x , y]}
        }else{
            canvas.onmousedown = (e) => {
            painting = true
            last = [e.clientX,e.clientY]
        }

        canvas.onmousemove = (e) => {
            if (painting === true) {
                drawLine(last[0],last[1],e.clientX,e.clientY)
                last = [e.clientX,e.clientY]
            }
        }

        canvas.onmouseup = () => {
            painting = false
        }
    }
    function drawLine(x1,y1,x2,y2) {
        ctx.beginPath();
        ctx.moveTo(x1,y1);
        ctx.lineTo(x2,y2);
        ctx.stroke();
    }


    </script>
</body>

</html>